In large endless non-metallic conveyor belts used to convey bulk material, there is a possibility of encountering a rip in the belt, for example, by a sharp object dropped thereon at the loading station. It is desirable promptly to detect such rips and, preferably, to shut down the conveyor belt upon such detection, thereby minimizing damage to the belt. One such conveyor belt rip detector is disclosed in U.S. Pat. No. 3,792,459. In such rip detector plural antennas, which may be single electrical conductors, are embedded in the belt transversely to its length at spaced-apart locations in the belt. An electrical signal is coupled by respective antennas from a transmitter to a receiver as the belt moves and the respective antennas pass in capacitive coupling relation with the transmitter and receiver at a rip detector station, and the receiver thus delivers an input signal to detector circuitry which interprets the same as an indication of satisfactory belt integrity. However, a broken antenna, for example at a plate where the belt has been ripped, will not couple the transmitter signal through to the receiver, and the detector then senses the same as an indication of the occurrence of a rip condition. The detector circuit in such patent is operative after the lapse of a predetermined time period corresponding to the passage of a given number of broken antennas past the rip detector station to produce a distinguishable output that activates an alarm and/or deactivates the conveyor belt drive.
A number of improvements for use in conveyor belt rip detectors are disclosed in co-pending U.S. patent application Ser. No. 960,424, filed Nov. 13, 1978, for "Monitor System System and Method for Detecting Sequential Events in a Cyclical Process", now U.S. Pat. No. 4,228,513, issued Oct. 14, 1980, and assigned to the same assignee as the present application. One of such improvements includes a means for detecting the progress of the conveyor belt to know when an antenna should be at the rip detector station. If there is no antenna present then, a prompt shut-down of the conveyor belt drive may be effected.
The disclosure of U.S. patent application Ser. No. 960,424, now U.S. Pat. No. 4,228,813, is hereby incorporated by reference.
Wear, stretching, contraction, dirt, other environmental conditions, etc. may cause a variation in the efficiency of signal coupling, whether of the capacitive, inductive, optical, or any other type of coupling, between the antennas (or other signal coupling means carried by the belt) and the transmitter and the receiver at a rip detector station. Such efficiency variation will vary the magnitude or other parameter of the input signal delivered from the receiver to the detector, which may detrimentally affect operation of the entire system.
Thus, it would be desirable to provide signal information to the detector at a relatively accurately controlled magnitude (or other parameter).
The system disclosed in application Ser. No. 960,424, now U.S. Pat. No. 4,228,513, operates in response to digital monitoring and control. Accordingly, it would be desirable to provide the aforesaid control, i.e. preferably gain control, function digitally.
Moreover, many prior signal control, i.e. preferably automatic gain control, circuits and the like have operated in a manner that provides a gradual signal variation in an analog fashion or in steps of equal increments, which may reduce the time efficiency of the control function.
Accordingly, it would be desirable to improve the time efficiency of the control function, such as an automatic gain control function.